The proposed studies are designed to provide cytological information on the distribution and quantity of the prolactin (PRL) cell population in the male rat adenohypophysis, in order to augment studies, by this investigator and others, on prolactin secretory patterns and regulation in the male. Specifically, immunological identification of PRL cells will be accomplished using the peroxidase antiperoxidase staining method. Quantitation of the stained cells will be carried out at the light microscopic level, in sectioned material and in tissue which has been enzymatically dissociated into single cell suspensions; both acutely dispersed cells and cells separated according to size-density via velocity sedimentation at unit gravity will be analyzed. Intracellular PRL levels will be assessed by RIA, and correlated with cell population size on aliquots of dispersed and separated cells. These studies will be extended to quantitative analysis of stained cells by laser light scatter flow cytometry. It is anticipated that development of this latter technique can be broadened and adapted for rapid, accurate analysis of immunoperoxidase stained cells of other types in adenohypophyseal and additional tissues. The technique would offer excellent collaborative potential within this laboratory for analysis of both rat and human tissues.